The invention relates to a method and a system in a wide area radio communication network, comprising at central stations, each cental station being assigned to one or more peripheral station.
To make possible for a plurality of users of wide area mobile or stationary radio systems to utilize common communication resources methods of time and/or frequency sharing (e.g. TDMA, ALOHA, CSMA, Polling, FDMA) have been developed. The first method developed was frequency sharing. The Nordic mobile telephone system NMT is based on this method. According to the frequency sharing method the users are allocated a certain channel at a certain frequency during the communication. Time sharing is a more modern method.
Digital wide area systems normally use time sharing, some times in combination with frequency sharing.
A drawback of the prior art methods for sharing resources is that the central station disposed in the center of the area must be able continuously to reach the peripheral stations spread out in each cell area or sector (e.g. within 360.degree. or 90.degree..; see FIGS. 1 and 2).
The quality of digitally transmitted signals is effected by reflection and diffraction, see FIG. 3. By using omni directional or sector directional antennas the transmission capacity is limited. This is a difficult problem especially in mobile systems.
Another drawback in current systems is that an ongoing information process between two stations results in transmission and reception in undesired directions. Small cell configurations such as those shown in FIG. 4 are common in radio area networks.
EP,A3,0201254 discloses a more developed radio communication system which utilizes spot beams, time division multiple access, and frequency-use to provide communication service from a central station to remote customers within a system service region. The central station provides multistage switching on intermediate frequency level to form a spotted beam in different directions so as to permit the respective sharing of radio transmitters and receivers over a major number of antenna transmitting and receiving ports. At the super central station, each section of the service area is covered by a different one of a raster of spot beams which are switched in accordance with a TDMA frame. A small number of transmission frequencies are re-used by different spot beams. The signal output energy is constant, regardless of the distance between the central station and the customer stations.
An object of the present invention is to overcome limitations and drawbacks of the prior art systems mentioned above. Another object of the present invention is to minimize interference between stations and to minimize the total power consumption of the system.